The present invention relates to the synthesis of adhesive compositions and more particularly to the synthesis of telechelic polymers of selected narrow molecular weight distribution for use in adhesives, coatings, and like applications. For present purposes, "telechelic" polymers are polymers that contain reactive end groups. "Polytelechelic" (co)polymers, then, contain two or more reactive pendant groups which often are end groups. For present purposes, "polymers" include homopolymers and copolymers (unless the specific context indicates otherwise), which may be block, random, gradient, star, graft (or "comb"), hyperbranched, or dendritic. The "(co)" parenthetical prefix in conventional terminology is an alternative, viz., "(co)polymer" means a copolymer or polymer, which includes a homopolymer.
Conventional free radical polymerization leads to synthesis of polymers with a fairly broad molecular weight distribution, Mw/Mn (weight molecular weight/number molecular weight), or polydispersity, in the range of 2.5 to 3. Number molecular weight (Mn) relies on the number of molecules in the polymer, while weight molecular weight relies on the weight of the individual molecules. See, e.g., Solomon, The Chemistry of Organic Film Formers, pp. 25, et seq., Robert E. Krieger Publishing Co., Inc., Huntington, N.Y. (1977), the disclosure of which is expressly incorporated herein by reference. The basic theory that applies to the control of the growth of the polymer chains and Mw/Mn ratios in a free-radical initiated polymerization reaction is well documented in the literature by P. J. Flory, JACS, Vol. 96, page 2718 (1952).
State of the art practice used to prepare polymers with a narrow molecular weight distribution in the range of, say, 1.05 to 1.4, rely on living polymerization techniques, such as anionic and cationic polymerization. These ionic living polymerization techniques have several limitations including, for example, restrictions on the types of monomers that can be polymerized, low temperature and purity process requirements, the inability to synthesize high molecular weight polymers, etc. Because of these constraints, ionic polymerization processes are limited to the synthesis of polymers based on styrene, isoprene, isobutylene, and like monomers to produce synthetic elastomers and thermoplastic rubbers.
Telechelic polymers prepared from either living polymers or condensation polymers, such as polyesters, for example, tend to be of low molecular weight, typically on the order of several hundreds to several thousands (e.g., 500-10,000). This low molecular weight limitation makes conventional telechelic polymers impractical for a variety of applications including, for example, adhesives.
Recent work on atom transfer radical polymerization (ATRP) has shown the potential of using this pseudo-living polymerization technique to prepare high molecular weight polymers based on acrylic monomers, vinyl monomers, and other common monomers which polymers exhibit a fairly narrow molecular weight distribution, say, in the range of 1.05 to 1.5. Molecular weights up to 10.sup.5 have been claimed to have been synthesized by ATRP techniques. See Patten, et al., "Radical Polymerization Yielding Polymers with Mw/Mn .about.1.05 by Homogeneous Atom Transfer Radical Polymerization", Polymer Preprints, pp. 575-576, No. 37 (March 1996); Wang, et al., "Controlled/"Living" Radical Polymerization. Halogen Atom Transfer Radical Polymerization Promoted by a Cu(I)/Cu(II) Redox Process", Macromolecules 1995, 28, 7901-7910 (Oct. 15, 1995); and PCT/US96/03302, International Publication No. WO 96/30421, published Oct. 3, 1996, the disclosures of which are expressly incorporated herein by reference.